Fuel system with a pressure pulsation damper

ABSTRACT

A fuel system for an internal combustion engine includes an outlet conduit having an internal volume and also having an exterior surface that is exposed to an environment. The fuel system also includes a pressure pulsation damper which includes a pressure pulsation damper wall made of a resilient and compliant polymer material which defines a pressure pulsation damper chamber. The pressure pulsation damper wall extends along, and is centered about, a pressure pulsation damper axis such that the pressure pulsation damper wall circumferentially surrounds the pressure pulsation damper axis, thereby defining the pressure pulsation damper chamber which is circumferentially surrounded by the pressure pulsation damper wall, the pressure pulsation damper wall having an inner wall surface which is in fluid communication with the internal volume of the outlet conduit and also having an outer wall surface which is exposed to the environment.

TECHNICAL FIELD OF INVENTION

The present invention relates to a fuel system for an internalcombustion engine, more particularly to such a fuel system whichincludes a pressure pulsation damper for mitigating pressure pulsationsof a fuel pump of the fuel system.

BACKGROUND OF INVENTION

Internal combustion engines which utilize liquid fuel are well known,for example, to provide propulsion in motor vehicles. Fuel systems fordelivering liquid fuel to the internal combustion engine are also wellknown. Such fuel systems typically include a fuel tank which holds avolume of fuel and one or more fuel pumps for pumping fuel from the fueltank to the internal combustion engine. It is known for the fuel pump totake any one of numerous forms which can generally be divided intopositive displacement pumps and regenerative pumps of which numerousvariations exist such as gerotor, turbine, roller vane, gear, and pistonpumps. Each type of fuel pump may produce pressure pulsations which, ifleft unmitigated, may produce noise that is undesirable. In somesituations, a fuel pressure regulator which regulates pressuredownstream of the fuel pump may inherently provide some damping of thepressure pulsations, however, the fuel pressure regulator may notaddress the pressure pulsations in the frequency range of concern.

What is needed is a fuel system with a fuel pressure regulator whichminimizes or eliminates one or more of the shortcomings set forth above.

SUMMARY OF THE INVENTION

Briefly described, a fuel system is provided for an internal combustionengine. The fuel system includes an outlet conduit having an internalvolume and also having an exterior surface that is exposed to anenvironment. The fuel system also includes a pressure pulsation damperwhich includes a pressure pulsation damper wall made of a resilient andcompliant polymer material which defines a pressure pulsation damperchamber. When the pressure pulsation damper chamber is filled with fuel,the pressure pulsation damper wall extends along, and is centered about,a pressure pulsation damper axis such that the pressure pulsation damperwall circumferentially surrounds the pressure pulsation damper axis,thereby defining the pressure pulsation damper chamber which iscircumferentially surrounded by the pressure pulsation damper wall, thepressure pulsation damper wall having an inner wall surface which is influid communication with the internal volume of the outlet conduit andalso having an outer wall surface which is exposed to the environment.

Further features and advantages of the invention will appear moreclearly on a reading of the following detailed description of thepreferred embodiment of the invention, which is given by way ofnon-limiting example only and with reference to the accompanyingdrawings.

BRIEF DESCRIPTION OF DRAWINGS

This invention will be further described with reference to theaccompanying drawings in which:

FIG. 1 is a schematic view of a fuel system in accordance with thepresent invention;

FIG. 2 is an exploded isometric view of a fuel pump of the fuel systemin accordance with the present invention;

FIG. 3 is a cross-sectional view of the fuel pump of FIG. 2;

FIG. 4 is an elevation view of an outlet conduit including a pressurepulsation damper of the fuel system in accordance with the presentinvention;

FIG. 5 is a cross-sectional view of the outlet conduit and pressurepulsation damper of FIG. 4;

FIG. 6 is the cross-sectional view of FIG. 5, now additionally showing awall of the pressure pulsation damper expanded as a result of a pressurepulsation; and

FIG. 7 is a cross-sectional view of an outlet conduit and two pressurepulsations dampers in accordance with the present invention.

DETAILED DESCRIPTION OF INVENTION

In accordance with a preferred embodiment of this invention andreferring initially to FIG. 1, a fuel system 10 is shown in schematicform for providing liquid fuel to an internal combustion engine 12. Fuelsystem 10 includes a fuel tank 14 defining a fuel tank volume 14 atherein for storing liquid fuel which is used to fuel internalcombustion engine 12. The liquid fuel stored in fuel tank 14 may begasoline, ethanol, a blend of gasoline and ethanol, diesel fuel, or anyother liquid fuel that may be used to fuel internal combustion engine12. A fuel pump 16 is disposed inside fuel tank 14 in order to conveyliquid fuel out of fuel tank 14 through an outlet conduit 18. Fuel pump16 is typically capable of supplying liquid fuel at a pressure in therange of 400 kPa to 600 kPa with a typical desired pressure being 500kPa. A pressure pulsation damper 20 is provided in fluid communicationwith outlet conduit 18 in order to mitigate pressure pulsationsgenerated by fuel pump 16 where the pressure pulsations, if leftunmitigated, may produce noise that is undesirable. While fuel system 10has been illustrated herein as including fuel tank 14, fuel pump 16,outlet conduit 18, and pressure pulsation damper 20, those of ordinaryskill in the art of fuel systems will readily recognize that otherelements may typically be included which may include, by way ofnon-limiting example only, a fuel filter (not shown) on the output sideof fuel pump 16 in order to filter contaminants out of the liquid fuelbefore the liquid fuel is conveyed to other components of fuel system10, a check valve (not shown) on the output side of fuel pump 16 anddownstream of the fuel filter in order to prevent backflow of fuel intofuel pump 16, and a fuel pressure regulator (not shown) on the outputside of fuel pump 16 and downstream of the check valve in order toregulate the pressure of the liquid fuel that is being conveyed out offuel tank 14 to a predetermined pressure. While fuel pump 16 has beenillustrated herein as being located within fuel tank 14, fuel pump 16may alternatively be located outside of fuel tank 14.

Fuel pump 16 may take any one of numerous forms, but will be describedherein by way of non-limiting example only with reference to FIGS. 2 and3 where fuel pump 16 is embodied as a regenerative fuel pump. Fuel pump16 generally includes includes a pump section 22 at one end, a motorsection 24 adjacent to pump section 22, and an outlet section 26adjacent to motor section 24 at the end of fuel pump 16 opposite pumpsection 22. A housing 28 of fuel pump 16 retains pump section 22, motorsection 24 and outlet section 26 together. Fuel enters fuel pump 16 atpump section 22, a portion of which is rotated by motor section 24 aswill be described in more detail later, and is pumped past motor section24 to outlet section 26 where the fuel exits fuel pump 16.

Motor section 24 includes an electric motor 30 which is disposed withinhousing 28. Electric motor 30 includes a shaft 32 extending therefrominto pump section 22. Shaft 32 rotates about a fuel pump axis 34 when anelectric current is applied to electric motor 30. Electric motor 30 willbe described in greater detail later.

With continued reference to FIGS. 2 and 3, pump section 22 includes aninlet plate 36, a pumping element illustrated as impeller 38, and anoutlet plate 40. Inlet plate 36 is disposed at the end of pump section22 that is distal from motor section 24 while outlet plate 40 isdisposed at the end of pump section 22 that is proximal to motor section24. Both inlet plate 36 and outlet plate 40 are fixed relative tohousing 28 to prevent relative movement between inlet plate 36 andoutlet plate 40 with respect to housing 28. Outlet plate 40 defines aspacer ring 42 on the side of outlet plate 40 that faces toward inletplate 36. Impeller 38 is disposed axially between inlet plate 36 andoutlet plate 40 such that impeller 38 is radially surrounded by spacerring 42. Impeller 38 is fixed to shaft 32 such that impeller 38 rotateswith shaft 32 in a one-to-one relationship. Spacer ring 42 isdimensioned to be slightly thicker than the dimension of impeller 38 inthe direction of fuel pump axis 34, i.e. the dimension of spacer ring 42in the direction of fuel pump axis 34 is greater than the dimension ofimpeller 38 in the direction of fuel pump axis 34. In this way, inletplate 36, outlet plate 40, and spacer ring 42 are fixed within housing28, for example by crimping the axial ends of housing 28. Axial forcescreated by the crimping process will be carried by spacer ring 42,thereby preventing impeller 38 from being clamped tightly between inletplate 36 and outlet plate 40 which would prevent impeller 38 fromrotating freely. Spacer ring 42 is also dimensioned to have an insidediameter that is larger than the outside diameter of impeller 38 toallow impeller 38 to rotate freely within spacer ring 42 and axiallybetween inlet plate 36 and outlet plate 40. While the pumping elementhas been illustrated as impeller 38, it should now be understood thatother pumping elements may alternatively be used, by way of non-limitingexample only, a gerotor, gears, or roller vanes. Furthermore, whilespacer ring 42 is illustrated as being made as a single piece withoutlet plate 40, it should be understood that spacer ring 42 mayalternatively be made as a separate piece that is captured axiallybetween outlet plate 40 and inlet plate 36.

Inlet plate 36 is generally cylindrical in shape, and includes an inlet44 that extends through inlet plate 36 in the same direction as fuelpump axis 34. Inlet 44 is a passage which introduces fuel into fuel pump16. Inlet plate 36 also includes an inlet plate flow channel 46 formedin the face of inlet plate 36 that faces toward impeller 38. Inlet plateflow channel 46 is in fluid communication with inlet 44.

Outlet plate 40 is generally cylindrical in shape and includes an outletplate outlet passage 50 that extends through outlet plate 40 in the samedirection as fuel pump axis 34 where it should be noted that outletplate outlet passage 50 is an outlet for pump section 22. Outlet plateoutlet passage 50 is in fluid communication with outlet section 26 aswill be describe in more detail later. Outlet plate 40 also includes anoutlet plate flow channel 52 formed in the face of outlet plate 40 thatfaces toward impeller 38. Outlet plate flow channel 52 is in fluidcommunication with outlet plate outlet passage 50.

Impeller 38 includes a plurality of impeller blades 56 arranged in apolar array radially surrounding, and centered about, fuel pump axis 34such that impeller blades 56 are aligned with inlet plate flow channel46 and outlet plate flow channel 52. Impeller blades 56 are eachseparated from each other by an impeller blade chamber 58 that passesthrough impeller 38 in the general direction of fuel pump axis 34.Impeller 38 may be made, for example only, by a plastic injectionmolding process in which the preceding features of impeller 38 areintegrally molded as a single piece of plastic.

Electric motor 30 includes a rotor or armature 64 which rotates aboutfuel pump axis 34 when an electric current is applied and also includesa stator 66 which remains stationary within housing 28 during operation.Electric motors and their operation are well known and will not bedescribed further herein.

In operation, inlet 44 is exposed to fuel in fuel tank 14 which is to bepumped to internal combustion engine 12. An electric current is suppliedto electric motor 30 in order to rotate shaft 32 and impeller 38. Asimpeller 38 rotates, fuel is drawn through inlet 44 into inlet plateflow channel 46. Impeller blade chambers 58 allow fuel from inlet plateflow channel 46 to flow to outlet plate flow channel 52. Impeller 38subsequently discharges the fuel through outlet plate outlet passage 50and consequently through outlet 62 which is connected to outlet conduit18.

Additional features of fuel pump 16 as embodied herein are described inUnited States Patent Application Publication No. US 2014/0314591 A1 toHerrera et al., the disclosure of which is incorporated by referenceherein in its entirety. While fuel pump 16 has been embodied herein as aregenerative fuel pump, fuel pump 16 may alternatively take other forms,which may be, by way of non-limiting example only a positivedisplacement pump such as those shown in United States PatentApplication Publication No. US 2016/0245284 A1 to Moreno et al. andUnited States Patent Application Publication No. 2014/0102417 A1 to Rosuet al., the disclosures of which are incorporated by reference herein intheir entirety. Furthermore, while fuel pump 16 has been illustrated asbeing located within fuel tank 14, it should be understood that fuelpump 16 may alternatively be located outside of fuel tank 14.

Now with particular reference to FIGS. 4-6, outlet conduit 18 includes atubular wall 18 a which extends along an outlet conduit axis 18 b suchthat an outlet conduit internal volume 18 c is defined within tubularwall 18 a, and consequently, outlet conduit 18 includes an interiorsurface 18 d which is in contact with the fuel in operation and alsoincludes an exterior surface 18 e which is exposed to, i.e. in directcontact with, an environment, which as embodied herein is fuel tankvolume 14 a. Outlet conduit 18 also includes a port 18 f which iscentered about, and extends along, a port axis 18 g where port axis 18 gmay be perpendicular to outlet conduit axis 18 b as shown, or mayalternatively be at some other angle relative to outlet conduit axis 18b. Port 18 f is tubular, thereby defining a port internal volume 18 htherein such that port internal volume 18 h is in fluid communicationwith outlet conduit internal volume 18 c. As shown in FIGS. 4-6, outletconduit 18 may be made of multiple components that are assembled to eachother, or alternatively outlet conduit 18 may be a single piece ofmaterial, for example, molded plastic. By way of non-limiting exampleonly, outlet conduit 18 may include a Tee fitting which defines port 18f and may also include two hoses connected to the Tee fitting, one ofwhich receives fuel from fuel pump 16 and the other of whichcommunicates fuel to internal combustion engine 12.

With continued particular reference to FIGS. 4-6, pressure pulsationdamper 20 includes a pressure pulsation damper wall 70 which is made ofa resilient and compliant polymer material which defines a pressurepulsation damper chamber 72. By way of non-limiting example only,pressure pulsation damper wall 70 may be made of a fluorocarbonmaterial, a fluorosilicone rubber material, or a plastic material.Pressure pulsation damper wall 70 may be sufficiently compliant suchthat prior to being filled with fuel supplied under pressure by fuelpump 16, pressure pulsation damper wall 70 may be limp and have anundefined shape, similar to a common party balloon prior to beinginflated. Consequently, the subsequent description will be provided withthe understanding that pressure pulsation damper wall 70 is filled withfuel under normal operating pressure of fuel pump 16.

Pressure pulsation damper wall 70 extends along, and is centered about,a pressure pulsation damper axis 74 which may be coincident with portaxis 18 g as shown where pressure pulsation damper wall 70circumferentially surrounds pressure pulsation damper axis 74. In thisway, pressure pulsation damper chamber 72 is circumferentiallysurrounded by pressure pulsation damper wall 70. Pressure pulsationdamper wall 70 includes an inner wall surface 76 which is in fluidcommunication with outlet conduit internal volume 18 c via port internalvolume 18 h. Pressure pulsation damper wall 70 also includes an outerwall surface 78 which is opposed to inner wall surface 76 such thatouter wall surface 78 is exposed to, i.e. in direct contact with, thesame environment as exterior surface 18 e, which as embodied herein isfuel tank volume 14 a. Inner wall surface 76 and outer wall surface 78are each a surface of revolution about pressure pulsation damper axis74.

Pressure pulsation damper wall 70 generally includes an attachmentportion 80, a first active portion 82 which extends from attachmentportion 80, and a second active portion 84 which extends from firstactive portion 82 such that first active portion 82 is located betweenattachment portion 80 and second active portion 84. Attachment portion80 includes an opening 86 therein which is fitted over port 18 f suchthat attachment portion 80 circumferentially surrounds, andcircumferentially engages, port 18 f in order to attach pressurepulsation damper wall 70 to outlet conduit 18. Attachment portion 80 maybe elastically deformed in order to be fitted over port 18 f, andconsequently, attachment portion 80 may apply a circumferentialcompressive force to port 18 f directed inward toward port axis 18 gand/or pressure pulsation damper axis 74. As should now be clear,attachment portion 80/opening 86 provides the only way into and out ofpressure pulsation damper chamber 72. Attachment portion 80 may be fixedto port 18 f, by way of non-limiting example only, using adhesives,ultrasonic welding, or clamping means such as a hose clamp or crimpedband (not shown), or combinations thereof. It should be understood thatif adhesives are used in order to secure attachment portion 80 to port18 f, attachment portion 80 is still viewed as circumferentiallyengaging port 18 f.

First active portion 82 diverges away from pressure pulsation damperaxis 74 in a first direction 88 along pressure pulsation damper axis 74.In other words, first active portion 82 increase in diameter when movingfrom attachment portion 80 toward second active portion 84. Conversely,second active portion 84 converges toward pressure pulsation damper axis74 in first direction 88 along pressure pulsation damper axis 74. Inother words, second active portion 84 decreases in diameter when movingfrom first active portion 82 away from both attachment portion 80 andfirst active portion 82. Second active portion 84 terminates at an apex90 such that pressure pulsation damper axis 74 intersects inner wallsurface 76 and outer wall surface 78 at apex 90 and such that pressurepulsation damper axis 74 passes through, and intersects, second activeportion 84 at apex 90. In operation, fuel pump 16 produces pressurepulsations which, if left unmitigated, may produce noise that isundesirable. However, since outlet conduit 18 is in fluid communicationwith pressure pulsation damper chamber 72, the pressure pulsations arepermitted to enter pressure pulsation damper chamber 72 which allows thepressure pulsations to expand first active portion 82 and second activeportion 84 of pressure pulsation damper wall 70, thereby increasing thevolume of pressure pulsation damper chamber 72 and also therebymitigating the pressure pulsations. FIG. 6 includes pressure pulsationdamper wall 70 shown expanded in phantom lines as a result of a pressurepulsation, however, it should be noted that the magnitude of expansionof pressure pulsation damper wall 70 has been exaggerated forillustrative clarity.

As is commonly known to those of ordinary skill in the art of fuelpumps, pressure pulsations of different frequencies are produceddepending on the design of the particular fuel pump. Consequently,pressure pulsation damper 20 may be tailored to mitigate the pressurepulsations produced by the particular fuel pump 16 used in fuel system10. Tailoring pressure pulsation damper 20 to mitigate pressurepulsations in particular frequency ranges may be accomplished by one ormore of the following: material selection for pressure pulsation damperwall 70, a thickness 92 of pressure pulsation damper wall 70, axiallength of pressure pulsation damper wall 70, profile of pressurepulsation damper wall 70/inner wall surface 76/outer wall surface 78,diameter of pressure pulsation damper wall 70, and cross-sectional area(perpendicular to pressure pulsation damper axis 74) of opening 86, aswell as altering the axial length of port 18 f and cross-sectional area(perpendicular to port axis 18 g) of port internal volume 18 h.Determination of the specifics of these features which result inmitigating pressure pulsations of the desired frequency may beaccomplished by one or more of finite element analysis (FEA),computational fluid dynamics (CFD) analysis, empirical testing, andtrial and error. Furthermore, if pressure pulsations in multiplefrequency ranges need to be mitigated, two or more pressure pulsationdampers may be provided as shown in FIG. 7 which shows an outlet conduit18′ which differs from outlet conduit 18 in that outlet conduit 18′ notonly includes pressure pulsation damper 20, but also includes a secondpressure pulsation damper 20′ such that pressure pulsation damper 20mitigates pressure pulsations in a first frequency range and pressurepulsation damper 20′ mitigates pressure pulsations in a second frequencyrange that is different than the frequency range. As can be seen in FIG.7, pressure pulsation damper 20′ includes the same general features aspressure pulsation damper 20, however, pressure pulsation damper 20′ hasbeen altered such that the profile, thickness, axial length, anddiameter of pressure pulsation damper wall 70′ have been alteredcompared to pressure pulsation damper wall 70 of pressure pulsationdamper 20. Similarly, a port 18 f′ to which pressure pulsation damper20′ is mounted differs from port 18 f in axial length andcross-sectional area of the inner passage.

Pressure pulsation damper 20 and pressure pulsation damper 20′ asdescribed herein provide a simple and economical way to mitigatepressure pulsations in fuel system 10. Furthermore, since pressurepulsation damper 20 and pressure pulsation damper 20′ are notconstrained and are exposed to the same environment as outlet conduit 18and outlet conduit 18′ respectively, pressure pulsation dampers 20, 20′are not limited by other materials for the frequency range of pressurepulsations that are to be mitigated.

While this invention has been described in terms of the preferredembodiments thereof, it is not intended to be so limited, but ratheronly to the extent set forth in the claims that follow.

We claim:
 1. A fuel system for an internal combustion engine, said fuelsystem comprising: an outlet conduit having an internal volume and alsohaving an exterior surface that is exposed to an environment; and apressure pulsation damper which includes a pressure pulsation damperwall made of a resilient and compliant polymer material which defines apressure pulsation damper chamber, wherein when said pressure pulsationdamper chamber is filled with fuel, said pressure pulsation damper wallextends along, and is centered about, a pressure pulsation damper axissuch that said pressure pulsation damper wall circumferentiallysurrounds said pressure pulsation damper axis, thereby defining saidpressure pulsation damper chamber which is circumferentially surroundedby said pressure pulsation damper wall, said pressure pulsation damperwall having an inner wall surface which is in fluid communication withsaid internal volume of said outlet conduit and also having an outerwall surface which is exposed to said environment.
 2. A fuel system asin claim 1, wherein when said pressure pulsation damper chamber isfilled with fuel, said pressure pulsation damper wall includes a firstactive portion which diverges away from said pressure pulsation damperaxis in a first direction along said pressure pulsation damper axis andalso includes a second active portion which extends from said firstactive portion and converges toward said pressure pulsation damper axisin said first direction along said pressure pulsation damper axis.
 3. Afuel system as in claim 2, wherein: said second active portionterminates at an apex; and said pressure pulsation damper axisintersects said second active portion at said apex.
 4. A fuel system asin claim 3, wherein said outer wall surface is a surface of revolutionabout said pressure pulsation damper axis.
 5. A fuel system as in claim1, wherein said pressure pulsation damper wall includes an attachmentportion which circumferentially surrounds, and circumferentiallyengages, a port of said outlet conduit.
 6. A fuel system as in claim 5,wherein said pressure pulsation damper wall includes a first activeportion which extends from said attachment portion and which divergesaway from said pressure pulsation damper axis in a first direction alongsaid pressure pulsation damper axis and said pressure pulsation damperwall also includes a second active portion which extends from said firstactive portion and converges toward said pressure pulsation damper axisin said first direction along said pressure pulsation damper axis.
 7. Afuel system as in claim 6, wherein: said second active portionterminates at an apex; and said pressure pulsation damper axisintersects said second active portion at said apex.
 8. A fuel system asin claim 1, further comprising a fuel tank defining a fuel tank volumetherein, wherein said fuel tank volume is said environment.
 9. A fuelsystem as in claim 1, further comprising: a second pressure pulsationdamper which includes a second pressure pulsation damper wall made of aresilient and compliant polymer material which defines a second pressurepulsation damper chamber, wherein when said second pressure pulsationdamper chamber is filled with fuel, said second pressure pulsationdamper wall extends along, and is centered about, a second pressurepulsation damper axis such that said second pressure pulsation damperwall circumferentially surrounds said second pressure pulsation damperaxis, thereby defining said second pressure pulsation damper chamberwhich is circumferentially surrounded by said second pressure pulsationdamper wall, said second pressure pulsation damper wall having a secondinner wall surface which is in fluid communication with said internalvolume of said outlet conduit and also having a second outer wallsurface which is exposed to said environment.
 10. A fuel system as inclaim 1, further comprising a fuel pump having an inlet, an outlet, anda pumping element which is configured to receive fuel from said inletand is configured to pump fuel to said outlet, wherein said outlet is influid communication with said internal volume of said outlet conduitsuch that said outlet is in series between said inlet and said pressurepulsation damper.
 11. A fuel system as in claim 10, wherein when saidpressure pulsation damper chamber is filled with fuel, said pressurepulsation damper wall includes a first active portion which divergesaway from said pressure pulsation damper axis in a first direction alongsaid pressure pulsation damper axis and also includes a second activeportion which extends from said first active portion and convergestoward said pressure pulsation damper axis in said first direction alongsaid pressure pulsation damper axis.
 12. A fuel system as in claim 11,wherein: said second active portion terminates at an apex; and saidpressure pulsation damper axis intersects said second active portion atsaid apex.
 13. A fuel system as in claim 12, wherein said outer wallsurface is a surface of revolution about said pressure pulsation damperaxis.
 14. A fuel system as in claim 10, wherein said pressure pulsationdamper wall includes an attachment portion which circumferentiallysurrounds, and circumferentially engages, a port of said outlet conduit.15. A fuel system as in claim 14, wherein said pressure pulsation damperwall includes a first active portion which extends from said attachmentportion and which diverges away from said pressure pulsation damper axisin a first direction along said pressure pulsation damper axis and saidpressure pulsation damper wall also includes a second active portionwhich extends from said first active portion and converges toward saidpressure pulsation damper axis in said first direction along saidpressure pulsation damper axis.
 16. A fuel system as in claim 15,wherein: said second active portion terminates at an apex; and saidpressure pulsation damper axis intersects said second active portion atsaid apex.
 17. A fuel system as in claim 10, further comprising a fueltank defining a fuel tank volume therein, wherein said fuel tank volumeis said environment.
 18. A fuel system as in claim 10, furthercomprising: a second pressure pulsation damper which includes a secondpressure pulsation damper wall made of a resilient and compliant polymermaterial which defines a second pressure pulsation damper chamber,wherein when said second pressure pulsation damper chamber is filledwith fuel, said second pressure pulsation damper wall extends along, andis centered about, a second pressure pulsation damper axis such thatsaid second pressure pulsation damper wall circumferentially surroundssaid second pressure pulsation damper axis, thereby defining said secondpressure pulsation damper chamber which is circumferentially surroundedby said second pressure pulsation damper wall, said second pressurepulsation damper wall having a second inner wall surface which is influid communication with said internal volume of said outlet conduit andalso having a second outer wall surface which is exposed to saidenvironment.